This invention relates to a novel re-usable thermal control structure and to a glass coating either for use in the structure or alone for thermal control. More particularly, the invention relates to a glass coating and a re-usable surface insulation (RSI) structure incorporating the coating and having primary application as a space shuttle heat shield, which structure has substantial advantages over prior art thermal control structures.
2. Description of the Prior Art
RSI compositions and structures suitable for use as a space shuttle heat shield are known in the art. Goldstein et al., U.S. Pat. No. 4,093,771 discloses such compositions and structures, which were proven in practice during the successful maiden flight of the space shuttle COLUMBIA. While the borosilicate glass coatings there disclosed exhibit satisfactory physical and optical properties in the convective heating environment expected during re-entry, it would be advantageous if coatings and structures could be provided that are able to withstand a higher use temperature, which have more stable long-term optical properties after repeated re-use during re-entry, and which have a lower strain in the coating induced by its processing.
Other thermal control coatings for space satellites or vehicles are also known in the art, but they are primarily designed for use at moderate temperatures, such as about 150.degree. F. These prior art thermal control coatings typically contain a pigment, such as zinc titanate, zinc, titanium oxide or zinc oxide, together with an organic or inorganic binder for ease of application and adherence on primarily non-porous skins of the satellites or vehicles. None of these types of prior art coatings were designed for use on re-usable re-entry space vehicles, since they are unstable at the high temperatures produced during re-entry, and are not suited for application to a low density silica substrate.
Thus, while the art of thermal control coatings and structures is a well developed one, a need remains for further development of RSI coatings and structures, especially adapted for use in space shuttle heat shields and similar applications.